The present invention relates generally to electro-hydraulic brake systems, and relates more specifically to a retainer for a brake master cylinder travel sensor magnet.
Master cylinders are commonly used in various applications, particularly in automobiles where they control various vehicular systems. For example, braking systems commonly known as brake-by-wire (BBW) or similar systems typically include a master cylinder that is isolated from the braking system. Such BBW systems rely on automatic electric or electric-hydraulic means to remotely activate the brake. Slave cylinders located at the automobile wheels typically actuate a braking process. Furthermore, one or more sensors positioned to monitor vehicle brake pedal position may control the process. The sensors measure pedal movement characteristics and relay this information to the brake system. The information is used to determine the appropriate braking force and is typically proportionate to a brake pedal force.
A potential shortcoming of current automobile master cylinder assemblies relates to positioning the sensors near the brake pedal. Situating the sensors on or near the brake pedal may require additional installation time and cost. Strategies for positioning a Hall effect sensor integral to a master cylinder are known thereby simplifying the packaging of the master cylinder-sensor assembly. The Hall effect sensors are capable of detecting minute perturbations in magnetic fields. These sensors, for example, may be used to precisely measure the movement of a neighboring permanent magnet that moves in response to a brake pedal motion.
The U.S. Pat. No. 4,918,921 issued Apr. 24, 1990 to Leigh-Monstevens et al. is an example of a coaxial push rod and ball screw nut drive for a master cylinder. In the Leigh-Monstevens patent, several forms of master cylinder assemblies are disclosed, including one embodiment for use in a vehicle braking system. In the preferred form, the assembly includes an electrically driven motor, a ball screw, and a piston positioned coaxially within a master cylinder bore. During operation, the motor armature rotates thereby driving the ball screw into the piston and slidably moving the piston within the bore. The assembly may include a Hall effect sensor carried by the master cylinder. As the armature spins, the Hall effect sensor detects passage of a series of rotating circumferentially positioned permanent magnet segments. The linear position of the ball screw and piston are determined based on the rotation count measured by the sensor.
The present invention is an assembly for sensing travel by a piston in a master cylinder. The assembly comprises a magnet and a retainer for retaining the magnet proximate the piston. An orientation screw engages an axial slot in the piston to inhibit rotation of the piston.
Accordingly, it is an object of the present invention to provide an assembly of the type described above that reduces tolerances associated with prior art brake pedals and brackets.
Another object of the present invention is to provide an assembly of the type described above that allows the use of a captured push rod, and eliminates any need for a hat-type retainer.
Still another object of the present invention is to provide an assembly of the type described above that uses a captured push rod.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.